Sexually selected infanticide in brown bears

Sexually selected infanticide (SSI) is a behavior where males kill dependent offspring, but not their own progeny, to gain access to breeding opportunities with the mother. SSI has mostly been documented in social species, such as primates and lions, however such behavior may operate differently in non-social species. The proposed study is based on the SSI hypothesis and the indirect effects of trophy hunting on the prevalence of SSI and its impact on population dynamics. We chose the non-social carnivore brown bear as study object, because very strong evidence for SSI has recently been found in this species. There is also evidence suggesting that trophy hunting is promoting such behavior in brown bears. SSI, its operating mechanisms, and its potential effects on bear population dynamics, have become a very controversial topic among researchers and managers due to the potential human impact, with clear implications for management and conservation. The goals of this study are to 1) conclusively determine whether SSI is operating in brown bear populations, and if so, document the mechanisms; 2) evaluate the effect of SSI on male and female lifetime reproductive success; 3) quantify the effects of hunting on the prevalence of SSI in a bear population and model its consequences for population dynamics, and 4) assess the effects of the presence/removal of dominant/important individuals, especially in small bear populations and their application for management and conservation. The general methods to study the proposed questions are the use of GPS-GSM radio-collars, genetic analysis to determine paternity, and the use of a long-term individual-based data set. The applicant will cooperate with the Scandinavian Brown Bear Research Project (SBBRP). The SBBRP has currently ~70 individuals radio-collared in its study area, 15 of these radio-collars are GPS-GSM collars. With an increase of GPS-GSM radio-collars the accurate movements, spatial and social relationships of individuals can be studied. The SBBRP has agreed 1) to grant access to its entire long-term data set; 2) to finance the analysis of all genetic material; 3) to finance the wages of the team capturing bears; 4) to organize a GPS ground station and SIM-cards for the GSM-GPS collars. The applicant has agreed 1) to finance the capture costs (helicopter-time, drugs) and GSM-GPS collars necessary for the study; 2) to finance the costs for SMS-transmission; 3) to finance a PhD-student to help carry out the project. Data will be analyzed using classic, individual-based and spatial statistical approaches and individual- based modeling. This study represents a unique opportunity to study infanticide and its evolution in a non-social species in the wild and determine the mechanisms behind this behavior. Understanding if and how SSI occurs in bear populations, the impact human harvest has on this behavior, and its potential effect on lifetime reproductive success and population dynamics has important implications for management and conservation. There are also ethical considerations. Society expects wildlife managers to know the effects humans have on hunted species; hunting seems not to affect just the behavior and ecology, but may even influence species on an evolutionary level. Answering the hypotheses presented in this proposal will give results for future needs.

A species or populations mating system is the product of sexual selection under a specific set of environmental conditions. Because reproduction is such as strong evolutionary force, understanding mating systems lies at the heart of behavioral ecology and can be important for conservation and management. This thesis deals with several aspects of the mating system of the brown bear (Ursus arctos). For infanticide to be a male reproductive strategy, i.e. SSI, three requirements need to be fulfilled, i) the killer does not kill his own offspring, ii) the victimized mother enters estrus earlier than if her cubs would have survived, and iii) the killer has a high probability to father the victimized mothers next offspring. We provided evidence for prediction ii, i.e., females rapidly (1-2 days) enter behavioral estrus after litter loss, which is in accordance with preliminary results from an endocrine approach. The vast majority (92%) of females entered estrus after litter loss during the mating season, mated, and gave birth during the next birthing season. Litter loss during the mating season reduced interlitter intervals of females in our study system by at least 50 % and can thus have significant reproductive advantage for males. We also documented infanticide (N = 8), infanticide attempts (N = 3), and litter loss due to unknown reasons (N = 1) between 2009 and 2011, and found that the patterns were in accordance to the SSI hypothesis. All cases occurred during the mating season, and all known perpetrators were adult males. Cub mortality during the mating season averaged 33 % between 2009 and 2011, and 92 % died because of infanticide. Our study yet lacked the data to document the genetic relationship between the killer, the victim and the victimized mothers subsequent offspring (prediction i and iii of the SSI hypothesis). However, genetic evidence for predictions i and iii has previously been documented in our study population (Bellemain et al. 2006a).We investigated how resource selection of various classes of bears was related to each other. We found that females with cubs-of-the-year (hereafter females/cubs) selected their resources spatially and temporally very different than conspecifics (especially adult males) during the mating season. For example, females/cubs used areas relatively close to human settlements, far from forest roads, in the least rugged landscapes, and more often in less dense vegetation (e.g., older forest types). Males often used areas close to forest roads, avoided human settlements, used areas in the most rugged landscapes more than expected, and always selected for the most dense habitat types. After the mating season, female/cubs shifted their resource selection towards a similar mode as their conspecifics; i.e. selecting areas far from settlements, in the most rugged terrain, and in denser habitat types. Our results suggest that females/cubs adapt their resource selection in space and time, most probably in response to the risk of SSI. We also show that females/cubs probably pay a nutritive cost during the mating season by selecting their resources in a spatiotemporally different way than conspecifics. This cost probably adds to the females cost of reproduction.